Goals of the 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE) program include developing new technology, new architecture and new methods for new LTE settings and configurations in order to provide improved spectral efficiency, reduced latency, better utilizing the radio resource to bring faster user experiences and richer applications and services with less cost.
FIG. 1 shows an overview of an Evolved Universal Mobile Telecommunications System (UMTS) Terrestrial Radio Access Network (E-UTRAN) 100 in accordance with the prior art. As shown in FIG. 1, E-UTRAN 100 includes three eNodeBs (eNBs) 102, however, any number of eNBs may be included in E-UTRAN 100. The eNBs 102 are interconnected by an X2 interface 108. The eNBs 102 are also connected by an S1 interface 106 to the Evolved Packet Core (EPC) 104 that includes a Mobility Management Entity (MME) 112 and a Serving Gateway (S-GW) 110.
FIG. 2 shows an LTE user-plane protocol stack 200 in accordance with the prior art. The protocol stack 200 is located in a wireless transmit receive unit (WTRU) 210 and includes the packet data control protocol (PDCP) 202, the radio link control (RLC) 204, the medium access control (MAC) 206 and the physical layer (PHY) 208. The protocol stack 200 may also reside in an eNB (not shown).
FIG. 3 shows an LTE control plane protocol stack 300 of the WTRU 210 of FIG. 2. The control plane protocol stack 300 includes the non-access stratum (NAS) 302 and a radio resource control (RRC) 304. Also included are the PDCP 306, RLC 308 and MAC 310, which together form the layer 2 sublayer 312.
The MAC entity may be reset or reconfigured as required. A reconfiguration occurs when one or more of the MAC entity's parameters, such as random access channel (RACH) parameters, are modified. A MAC reset procedure may be performed at handover, cell-reselection, radio resource control (RRC) connection re-establishment and upon the WTRU moving from RRC connected state to RRC idle state.
The parameters for a MAC entity may be reconfigured by the upper layers. When a RACH parameter is reconfigured by an upper layer, the WTRU may start using new RACH parameters the next time the random access procedure is initiated. This may include if an available set of physical random access channel (PRACH) resources for the transmission of the random access preamble and their corresponding radio access-radio network temporary identifiers (RA-RNTIs) are modified, for example. This may also include modifying groups of random access preambles and a set of available random access preambles in each group. Other parameters may be modified, such as the thresholds required for selecting a group of random access preambles, the parameters required to derive the transmission time interval (TTI) window, the power-ramping factor, the maximum preamble transmission power, the initial preamble transmission power, the maximum number of message hybrid automatic retransmission request (HARQ) transmissions, the preamble transmission counter, and the backoff parameter, for example. For other modified parameters, the WTRU may start using the reconfigured value of the parameter immediately.
FIG. 4 shows a method of resetting a MAC entity 400 in accordance with the prior art. In step 402, the WTRU flushes all hybrid automatic repeat request (HARQ) buffers. At step 404, the WTRU initializes a counter, CURRENT_TX_NB, which counts the number of transmissions that have taken place for the MAC protocol data unit (PDU) currently in the buffer. The WTRU sets the counter to zero for all HARQ processes. At step 406, the disassembly and demultiplexing entity are flushed. At step 408, the WTRU will detect if a random access procedure is ongoing. If so, at step 410, the WTRU will abort the ongoing random access procedure. At step 412, the WTRU will flush a message buffer, and at step 414, it will initialize the preamble transmission counter to zero. At step 416, the WTRU may consider the contention resolution timer to be expired and discard the cell radio network temporary identifier (C-RNTI). The contention resolution timer specifies the number of consecutive physical downlink control channel (PDCCH) subframes that the WTRU monitors on the PDCCH after the uplink message containing the C-RNTI MAC control element or the uplink message associated with WTRU contention resolution identity submitted from a higher layer is transmitted. At step 418, the WTRU may adjust a number of timers, such as the time alignment timer, the on-duration timer, the DRX inactivity timer, the DRX retransmission timer, the DRX short cycle timer, the periodic buffer status report (BSR) timer and the power head room (PHR) timer, for example.